Aircraft control system

This invention control system having: means ( 12 ) for detecting an irregularity in aircraft handling during flight; means ( 18 ) for causing temporarily a rigid body excitation in at least a portion of the aircraft; means ( 20 ) for monitoring an actual response to the excitation; means ( 22 ) for comparing the actual response and a target response to the rigid body excitation; and means ( 14 ) responsive to an output from the comparison means for determining the need for a modification of the current flight plan and for generating a corresponding control output. The invention also provides a corresponding method for controlling an aircraft.